Um, I'm within the same general weather pattern as Chicago, and the notion that Chicago, or Medinah, was dealt a bad hand due to wet weather is, so to speak, all wet. It's been a normal-to-slightly-dry summer here in the Upper Midwest.
Adam, I think the notion of relying on scientific data and long-term weather patterns to determine sites for majors is just plain silly. I used to hang around a bunch of meteorology students back during my days living near Penn State (paging Kyle Harris), and they were a bunch of really smart folks, and they used to laugh at the notion that weather could be predicted months or years in advance, much less days. Weather patterns can be narrowed down to the four seasons, and yes, it's drier in Mullen, Neb., than Chicago, but you can't do much better than that. It's the luck of the draw. Witness what happened at the PGA a few years ago at Hazeltine -- anyone remember that 3rd round front that moved through, complete with 25-35 mph winds? THAT was a fun round of golf to watch, largely because of unpredictable weather. Compare to the US Women's Open at Newport -- a great lost opportunity to see a truly firm and fast course in its usual state, due to unprecedented East Coast rain (it was much, much browner there when Tiger won the AM there in '95).
And let's face it -- both the USGA and the PGA have a strong financial interest in rotating these majors around major geographic/populated regions of the country. Why else would they put the Open at Torrey Pines? Because Riveria can't handle it, they can't keep going back to Pebble and Olympic, and they want Southern California (broadly speaking) to have a slice of the major pie, for commercial/sponsor tie-ins.
I do endorse the idea of more majors at Kiawah, however.